Automatic counterbalancing means for load lifting apparatus



Oct. 17, 1950 s. E. TANGUY 2,526,613

AUTOMATIC couu'masmcmc mums FOR LOAD LIFTING APPARATUS 5 Sheets-Sheet 1 Filed Jan. 30, 1947 & 3 A2 6 A? 50 250.

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= AUTOMATIC COUNTERBALANCING MEANS FOR';LOAD LIFTING APPARATUS I 5 Sheets-Sheet 2 Filed Jan. 30, 1947 '2 54 1 i 5 a; 62 66 &

G. E. TANGUY 2,526,613 AUTOMATIC, cou ALANCING MEANS FOR LOAD LIFTING APP Oct. 17, 1950 ARA'I'US 5 Sheets-Sheet 5 Filed Jan. 30, 1947 7 r h ,5) r% Oct. 17, 1950 s. E. TANGUY Amolm'rrc COUNTERBALANCING MEANS FOR LOAD LIFTING APPARATUS Filed Jan. 30, 1947 5 Sheets-Sheet 4 G. E. TANGUY 2,526,613 AUTOMATIC COUNTERBALANCING MEANS FOR 1.01m LIFTING APPARATUS Oct. 17, 1950 5 Sheets-Sheet 5 Filed Jan. 30, 1947 m .ow p kfi /mb o @N\ QT ON .Qw E T QT MUN counterweight alone,

Patented Oct. 17, 1950 UNITED STATE AUTOMATIC COUNTERBALANCING MEANS FOR LOAD LIFTIN APPARATUS George E. Tanguy, Syracuse, N. Y.

Application January 30, 1947, Serial No. "125,397 (01. 212-49) 9 Claims.

The present invention relates to load lifting and handling apparatuses such as cranes, shovels, and the like and more especially to counterbalancing means therefor.

The primary object of the invention is to provide a counterbalancing mechanism for load lifting and handling apparatuses of the type above referred to, which is fully automatic, efficient and quick in its operation, and which may be readily applied to cranes, shovels and similar machines of conventional or existing design without material modification or revamping of the basic machine structure.

A further object of the invention is to provide a practical and improved counterbalancing mechanism for machines of the aforementioned type,

which will automatically compensate for variable loads and keep the machine in constant balance, thereby avoiding overturning hazards and increasing the capacity of the machine.

While my invention may be applied to various and sundry types and makes of load lifting and handling machinery, it is especially applicable,

bu't not limited to, cranes and shovels which are mounted on crawlers and trucks which are more frequently than not operated on uneven ground .or in positions other than a perfectly level or horizontal position. By virtue of the novel and improved construction and arrangement of the automatic control features of the present invention, it is not necessary to maintain the machine in a level or horizontal position. A still further object of the invention is to provide' a novel and impdoved movable counterweight which may be applied to a crane or shovel without-necessitating the removal or revamping of the usual stationary counterweight with which .such machines are equipped, said movable counterweight being so designed as to provide equal distribution of weight all around the center pin or, axis of swing of the machine when the movable counterweight assumes a no-load position,

thereby permitting operation of the machine under the influence of the regular or stationary However, my movable counterweight is further designed and so. con- ;trolled, preferably automatically, that it will maintain the machine in constant balance, both.

lower the center of gravity of the machine, and which is capable of being mounted so as to always lie within the confines of the swinging frame 01 the machinevthroughout the complete range of its load-compensating movements. This feature attains the important advantages of' making the present invention applicable to machines where space and clearances are limited, and eliminating any increase in tail swing, which, if present, would preclude its use when the' machines are operated in close quarters, or with truck mounted machines where the truck cab or other equipment would interfere with the swing.

The invention also contemplates'the provision of anovel and improved control system for auto: matically actuating movable load-compensating counterweights for machines of the character above described, said control system being unaffected by the working position of the machine,

and assuring smooth and rapid movement of the counterweight in response to variations of load imposed on the machine.

Other and further objects and advantages of the invention will be hereinafter describedand the novel features thereof defined in the appended claims.

In the drawings:

Figure 1 is a fragmentary view, partly in top plan and partly in horizontal section, showing the adjustable load-compensating counterweight and certain of the operating mechanism therefor, as applied to a crane or shovel of the truck-mounted type;

Figure 2 is a fragmentary vertical sectional view taken on the line 22 of Figure 1;

Figure 3 is a fragmentary vertical sectional view taken on the line 3-3 of Figure 1;

Figure 4 is a diagrammatic View showing, by way of a typical illustration, certain of the operating andcontrol mechanismsfor actuating the load-compensating counterweight;

Figure 5 is-an enlarged sectional detail view of the hydraulic control valve and its associated electromagnetic equalizing. or balancing device which form a part of the control mechanism shown in Figure 4, said control valve and the balancing device being illustrated in their neutral 7 orholding positions -to maintainv the load-com- ,with aswell as without load, so as, to remove all .strain and stress from the swing assembly, cen-' ter pin, rollers and other parts normally affected by load strains or stresses when employing the usual stationary counterweight alone.

Another object of the invention is to provide an improved movable load-compensating counterweight which is compact in form, serves to pensating counterweight in a condition of rest;

Figure 6 is a view generally similar to Figure 5, showing the control valve and balancing device in their increased load positions, serving to cause movement of the counterweight in a directionto compensate for an increase in load on the machine;

Figure 7 is a view generally similar to Figures 3 5 and 6, showing the control valve and balancing device in their decreased load positions;

Figure 8 is an enlarged fragmentary vertical sectional view taken through one of the circuitclosing switches which forms a part of the electrical control circuit which automatically controls the movement of the counterweight in response to variations of the load;

Figure 9 is a sectional view generally similar to Figure 8, showing a modified form of circuitclosing switch;

Figure 10 is an enlarged sectional view taken through one of the circuit-breaking switches which also forms a part of the electrical control circuit;

Figure 11 is a diagrammatic view of the complete control mechanism or system, as applied to a load lifting or handling apparatus of the floating house roller type; and

Figure 12 is a diagrammatic view, generally similar to Figure 11, of a modified control mechanism or system, as applied to a load lifting or handling apparatus of the stationary house roller type.

Like reference characters designate correspond ing parts in the several figures of the drawings, wherein! generally denotes the body or house of a load lifting or handling apparatus such as a crane, shovel, or the like, said house being suitably mounted upon a crawler base or upon a truck generally indicated at 2. The house I is provided at one end with a stationary counterweight generally designated 3, which normally serves to counterbalance the machinery usually disposed within the house and a boom (not shown) which extends from the opposite end of the house, and which may be equipped with a shovel or other load lifting or handling equipment adapted to be controlled in the well known manner by the machinery within the house. It will be understood that the details of the machinery and the load lifting and handling equipment are immaterial to the present invention, and hence need not be specifically described. For the purposes of this description, it may be said that the element designated I generally represents a crane, shovel, or similar machine of conventional or other suitable design, which is mounted to swing about a vertical aXis generally represented by the vertical center pin 4 extending upwardly from a base plate 5, with rollers interposed between the base plate 5 and the bed of the house I, said rollers being of the floating house roller type, as indicated in Figures 1, 2 and 11, in which the rollers are designated 6, or of the stationary roller type, as indicated at 'I in Figure 12.

The problem which is common to machines of this type is that becauseof angular movements of the boom which is usually pivotally attached to the swinging house I so that it may be raised or lowered as desired, loads of the same weight may therefore be disposed at different distances from the center pin 4 which is the axis of swing. Consequently this will create different torques or moments of force tending to tip the machine relative to its vertical axis of swing. Since the load and its horizontal distance from the axis of swing determines the value of this torque, and since these two factors often vary rapidly and without close control of the operator, it is difficult for the operator to prevent the torque from rising to such a value as to tend to overturn or topple the machine. This is especially true when the machine is being operated on unlevel ground or in any working position other than perfectly level or horizontal.

It is the purpose of the present invention to provide a counterbalance and an operating mechanism therefor for varying the position of the counterbalance automatically to maintain the machine in balance irrespective of variations in the load, and irrespective of whether such variations are caused by variations of the dead weight of the load itself, or variations of the angular position of the boom. The automatic control mechanism is so designed as to be responsive to slight tilting movements of the swinging portion of the machine, or slight angular deviations of the body from its normal horizontal position.

.Preferably, the control mechanism embodies both hydraulic and electrical instrumentalities, which have the advantage of simplicity, ease, rapidity, and smoothness of operation, compactness of form, and lightness of weight, durability, and efficiency of operation.

In the embodiments of the invention as illustrated in the drawings by way of example, my new counterbalance includes a movable counterweight designated 8 which is of an appropriate massive weight according to the size and construction of the machine to which it is applied, said counterweight being of U-shape or horse-shoe shape so that the weight thereof may be equally distributed around the axis of the center pin 4 when the counterweight assumes a position at the limit of its forward movement towards the load or boom end of the machine. The counterweight 8 is provided on its lower surface with a plurality of rollers a which ride upon tracks, Ill, I0, extending longitudinally of the house I at opposite sides thereof, and a central longitudinal track I! disposed intermediate the tracks ID, ID. The tracks and the'countc'rweight 8 are all preferably disposed beneath the bed of the house I so as to be out of the way and so that nothing may interfere withthe free movement of the counterweight 8 forwardly and rearwardly relative to the axis of swing of the machine as represented by the center pin 4. To assist in guiding the counterweight 8 in its forward and rearward movements, the counterweight is preferably recessed on its opposite sides, as indicated at I2, I2, and the tracks I0, I I] may have the form of Z-shaped bars which extend into the recesses I2, I2, as clearly shown in Figure 3 of the drawings.

Movement of the counterweight'B may be attained in any suitable manner, but preferably by means of a pair of hydraulic jacks generally indicated at I 3, I3. Said jacks are respectively located on opposite sides of the longitudinal center,

of the machine, and each jack has its forward end suitably attached to the house I, a indicated at I4, I4, and its rear end attached to the counterweight, as indicated at E5, I5. Jacks I3, I3 may be of any suitable construction or of conventional form which usually includes a cylinder and a piston therein, the cylinder being attached to the house I as indicated at I4, and the piston having a piston rod extending from the cylinder for conncction to the counterweight at I5. Each jack is of the double acting type so that the piston may be powered in either direction to cause movement of the counterweight 8 both forwardly and rearwardly.

In order to operate the hydraulic jacks I3, I 3, some suitable control means must be provided. Said control means may be of any suitable type, but I preferably employ a hydraulic system of the type disclosed in Patent No. 2,304,380, granted December 8, 1942, or the equivalent of such a system. The details of the hydraulic system are fully shown and described in the aforesaid patent and need not be repeated herein. Suffice it to say that the system includes a control valve unit gen-. erally designated l6, having an inlet pipe l1 and an outlet pipe l8 connected respectively to an inlet and outlet formed in the housing of the control valve unit. The inlet pipe I1 is connected to the outlet of a conventional hydraulic pump generally designated l9. which may be of the gear pump type, said pump having an inlet pipe which is submerged in a hydraulic fluid 2|, such as oil, contained within a receptacle or tank 22.

Shiftably mounted within the housing of the control valve unit It, is a control valve member generally designated 23 which serves to controlthe distribution of the hydraulic fluid in the system. In Figure 5 of the drawings, the control valve 23 is shown in the neutral or hold position which causes the hydraulic fluid to be circulated from the pump l9 through the control valve unit Hi from which it is discharged through the pipe i8 back into the tank 22. By shifting the control valve '23 to the position shown in Figure 6, which may be termed the increased load position, the hydraulic fluid will be forced by the pump l9 through the control valve unit l6 into a conduit or pipe 24 which is in turn connected to the forward ends of both hydraulic jacks l3, l3, the connection between the pipe 24 and, the cylinders of the hydraulic jacks being preferably established through flexible conduits which serve to admit the hydraulic fluid at the front side of the pistons so as to cause the pistons to move rearwardly in their cylinders, which in turn causes a rearward movement of the counterweight 8. In this position of the control valve 23, the hydraulic fluid behind the pistons in the jacks i3, 1 3 is permitted to flow out of the cylinders through the flexible conduits 26 which are in turn connected by a pipe 21 to the control valve unit I6 which permits the return of this hydraulic fluid to the tank 22 through the discharge pipe 18. r

In Figure '7 of the drawings, the control valve 23 is shown in the'decrease load position'which serves to cause the hydraulic fluid to be forced by the pump [9 through the pipe 2'5 and conduits 25 into the rear ends of thecylinders of the hydraulic jacks l3, l3, thereby causing forward movement of the pistons in the jack cylinders, and consequently forward movement of the counterweight 8. During such forward move ment, the position of the control valve 23 allows the hydraulic fluid at the forward side of the pistons in the hydraulic jacks l3, 13 to return through the conduits 25, pipe 24, to the control valve unit l6, from which the hydraulic fluid is gischarged through the pipe I8 into the tank 2. I t will be undersood from the foregoing that it is necessary to-shift the control valve 23 to either the increased load position shown in Figure 6, or the decreased load position shown in Figure '7, in order to produce movement of. the counterweight 8, but with the control valve 23 restored to its neutral or hold position shownin Figure 5, all movement of the counterweight will be discontinued andthe counterweight will remain at rest in whatever position it is in when the control valve 23 is moved to the neutral or hold position. It is, therefore, necessary'to' provide suitable means for imparting movementsin either directionto the control 'valve 23, and for parts of the circuit closing device 39.

5 system which includes circuit making and breaking instrumentalities which are automatically operable responsive to variations in load on the machine, and an electromagnetic valve positioning device. The electrical system will be best understood from reference to Figures 11 and 12, the former of which will be first described. In this system, 28 designates a suitable source of electrical energy, such as a battery, one side of which is grounded by a conductor 29 leading to a ground which may be the frame of the machine. To the opposite side of the battery28 is connected a circuit closing device or switch unit generallyindicated at 30 as more fully shown in Figure 8 of the drawings. As will be seen in the latter figure, the device 30 includes a housing 3| which is supported b a bracket 32 which is in turn fixed to the swinging house I of the machine. Slidably mounted for movement in an upward and downward direction in the housing 3| is a plunger 33 which is provided at its upper end with an enlarged head 36 which forms a seat for one end of a coil spring which surrounds the upper end of the plunger. The opposite end of the coil spring rests upon a flange or shelf 38 which extends radially inwardly from the housing 3|. Below the spring, the plunger 33 is provided with an annular flange 3! which carries a pair of electrical contacts 38, 38 which are arranged for cooperative engagement with a corresponding pair of flxed contacts 39, 39, the latter being suitably insulated from the housing 3! From one of the fixed contacts 39 a conductor 40 leads tothe battery 28, and from the other fixed contact 39, a conductor 4! leads tov one side of a circuit breaking device generally indicated The plunger 33 mentioned above extends downwardly below the housing 3! of the circuit closing device 30, and the lower end of the plunger is preferably threaded for screw threaded engagement within a sleeve 43 having a nut 4&- formed integrally therewith at its upper end. A jam nut 45 also is threaded on the plunger 33, and when screwed up against the nut M, serves to lock the sleeve 53 in any position of adjust-- ment lengthwise of the plunger 33. Within the lower end of the sleeve E3 is a second plunger 4& having an enlarged head 41 on the upper end? thereof and forming a seat for one end of a second coil spring d8 arranged within the lower end of the sleeve. The opposite end of the spring 48' seats against an inwardly turned flange is at the bottom end of the sleeve A3. The plunger Q6 is therefore yieldingly connected to the plunger 33 so that when the plunger 33 has been moved downwardly to bring the contacts 38 and 39 into abutting engagement with each other, the plunger Mimay continue its downward movement without causing damage to the contacts or other At its lower end, the plunger 46 is laterally extended, as indicated at 50, and then upwardly extended as indicated at 5|. At the upper end of the upwardly extending arm 5!, there is provided a roller 52 which is rotatably mounted in a bracket 53 suitabl fixed to the arm'iii. The roller 52 bears against'the lower side of the base plate 5 on which the body of the crane, shovel, or other load lifting or handling apparatus, as the case may be, is mounted for swinging movements about the center pin 4 previously described.

Due to the spring 35, the contacts 38, 38 of the device 38 are normally spaced slightly from the contacts 39, 39, and will remain so spaced as long as the machine remains in a condition of balance during its operation, and the electrical circuit will be broken. However, as soon as the machine tends to get out of balance as the result of an increase in load, the machine will tend to tip forwardly, which in turn causes a slight upward movement of the rear end of the swinging body of the machine to which the device 30 is fixed, thereby depressing the roller 52 and the arm 56 and resulting in downward movement of the plunger 33 and closing of the contacts 38, 35. When the electrical circuit is thus closed, current may flow from the battery 28 through the circuit closing device 39, to the circuit breaking device the latter being in the nature of a normally closed switch device as i1- lustrated in detail Figure 10, and from the switch device :22, the current continues through a conductor leading from the switch device 42 to one side of one end of a control valve positioning device 58, the opposite side of the winding 55 being suitably grounded to complete the electrical circuit.

The positioning device generally designated 56 is best shown in Figures 5 to 7 inclusive, from which it will be seen that it includes two spaced housings 5T, 5?, each of which has an electrical winding at the outer end thereof, designated 55, as previously referred to. Within each housing 51, 51 is an armature 58, 58 of magnetic material, said armatures being movably mounted within their respective housings, and being rigidly connected together by a connecting bar 58, which is in turn connected by a bar 63 to the outer end of the control valve 23 of the hydraulic con trol valve unit it). Between each of the armatures 58 and the end wall of the housing opposite to the winding 55 is a coil spring 5%, said springs being of equal tension and serving to normally space the respective armatures 58, 58 equidistantly from their windings 55, Accordingly, when no current is flowing in the clr cuit just described, the springs 6i, 6! will hold the armatures 58, 58 in their neutral positions, respectively spaced from the windings 55, 55, which in turn causes the control valve 23 to assume a neutral or holding position as illustrated in Figure 5 of the drawings. When the circuit is closed by the circuit closing device 30, responsive to an increase in load, as above described, the winding 55 at the lefthand end of the control valve positioning device 53 will be energized, thereby attracting the armature 53 at the lefthand end of the positioning device causing movement of the bar 66 and the control valve 23 to the left until the control valve assumes the position shown in Figure 6 of the drawings, which is the increased load position. The control valve 23 will remain in this position so long as the machine is unbalanced, and the counter-weight 8 will continue to move to the left, as viewed in Figures 1 and 2 of the drawingsuntil the counterweight reestablishes a balance of the machine, at which time the contacts of the circuit closing device 3*? will open and break. the electrical circuit, thereby deenergizing the winding 55 at the lefthand end of the valve positioning device 55. When such deenergization occurs, the springs 5!, 5% will cause the armatures 58, 58 to move to the right, restoring the control valve 23 to the neutral or hold position shown in Figure 5, which in turn causes movement of the counterweight 8 to be discontinued, and the counterweight remains in a condition of rest until the machine again becomes unbalanced.

an electr cal winding 55 at 8 will be seen from the circuit closing device 30 is represented as being mounted on the swinging part of the machine, with the device 30 located at the side of the vertical axis of swing which is opposite to the side at which the load is imposed on the machine. load, a second circuit closing device designated 35", which may be identical with the device 30, is mounted on the swinging part of the machine in opposed relation to the device 30. This second device 38 is connected to the battery 28 by a conductor 46', and also to a second circuit breaking switch 42" which is identical to the switch t2, the switch 42' being in turn connected by a conductor 54' to a winding 55 at the righthand end of the control valve positioning device 56, the opposite side of the winding 55 being suitably grounded to complete the circuit. The operation under conditions of decrease load is identical with that previously described, except that the circuit making device 3t" serves to close the circuit when the front end of the swinging body of the machine tends to move upwardly by reason of the decrease in load on the machine or raising of the boom, and when the circuit is closed under these conditions, the winding 55 at the righthand end of the control valve positioning device 55 will be energized, causing the control valve 23 to be shifted to the right as shown in Figure 7. When this occurs, the hydraulic system functions to move the counterweight 8 to the right, as viewed in Figures 1 and 2, and the counterweight continues such movement until it balances the machine, at which time the circuit closing device 36 will automatically open the circuit and deeriergize the winding 55 at the righthand end of the control valve positioning device 55, and the control valve 23 will automatically shift to the neutral or holding position shown in Figure 5, under the influence of the springs 6|, 6!, at which time the counterweight will discontinue any further movement and remain in a condition of rest until the machine again gets out of balance.

As previously mentioned, the circuit breaking devices or switches 42, 42 may be identical in construction, and may have any suitable form. Preferably, the construction conforms to that illustrated in Figure 10, from which it will be seen that each switch is of the normally closed pushplunger type. Each switch construction embodies a housing 62 in which is slidably mounted a plunger or pin 83 which projects at one end from the end of the housing, and terminates at its opposite end in an enlarged head 64 disposed within the housing and seating against one end of a coil spring 55 which is disposed between the head 64 and the opposite end of the housing. The head 64 carries a contact bar or ring 66 which is normally urged by the spring 65 against a pair of spaced contacts t7, 5?, suitably mounted within the housing 62 and insulated therefrom. In the case of the switch designated 42, one of the contacts 61 is connected with the conductor 54, and the other contact 57 is connected with the conductor 4| As will be best seen from reference to Figuresl and 2, the switch 42 is mounted in the swinging body of the machine at the rear end thereof in such a position that the projecting plunger 63 is disposed in a position to be engaged by the back end of the counterweight 8 when the counterweight reaches the limit of its rearward movement. The other switch 42' is similarly mounted reference to Figure 11,.

In order to take care of decreases inv in the swinging body of the machine so that its projecting plunger 63 will be engaged by the forward side of the counterweight 8 when the counterweight reaches the limit of its forward movement. In either case, when the counterweight 8 engages the plunger 63,.it will depress the plunger against the action of the spring 65, which will in turn open the circuit to the windings 55, 55 of the valve positioning device 56, thereby allowing the control valve 23 to assume its neutral or holding position. The two switch devices 42, 42' therefore serve as limit switches or safety switches and will remain closed excepting under abnormal conditions.

In Figure 12, I have shown a somewhat modified arrangement of the electrical system which is more particularly applicable to machines of the stationary house roller type. Basically, the system is the same, and differs from the system of Figure 11 in the use of a somewhat different form of circuit closing device which is substituted for the devices designated 30, 3!) in Figure 11. In the modified arrangement, there are two circuit closing devices respectively designated 300 and 300, corresponding to the devices 30 and 30, said devices being suitably mounted on the swinging body of the machine, butin the reverse positions respecting the axis of swing. All other parts of the system in Figure 12 are identified by the same reference characters as in Figure 11. The circuit closing devices 300, 300' are identical with each other, and the details thereof are more particularly shown in Figure 9, from which it will be seen that the device includes a housing 3H1 within which is slidably mounted a plunger 330 which supports at its upper end a contact bar or plate 380, suitably insulated from the plunger, and disposed to engage a pair of stationary spaced contacts 390, 390. The plunger 330 extends beyond the lower end of the housing 3 l (I, and the lower end of the plunger is preferably threaded for adjustable threaded engagement with a sleeve 430 connected to the lower end thereof, said sleeve having a nut 440 integrally formed therewith on its upper end and coacting with a also threaded on the lower end of the plunger. Above the nuts, the plunger is provided with an annular flange 45! which serves as a seat for one end of a coil spring 350 encircling the plunger, and having its opposite end seated against the lower end of the housing 3"]. The spring 350 thus serves to normally urge the plunger 330 in a downward direction, spacing the contact plate 380 from the contacts 390, 390, so that the circuit is normally open. In order to limit the downward movement of the plunger 330, it is provided with a flange 310 disposed within the housing 3H) for abutting engagement with an internally extended shelf or ledge 360.

Within the lower end of the sleeve slidably disposed therein is plunger having an enlarged head 410 on its upper end against which bears the lower end of a coil spring 480 disposed within the sleeve 43!}, the upper end of the spring bearing against the lower end of the plunger 33!]. 7 Thus, the plunger 460 is yieldably connected to the plunger 33!} so as to allow a limited yielding movement of the plunger 460 after the contacts 380, 39il'are closed. Rotatably mounted on the extreme lower end of the plunger A60 is a roller 52!]. The circuit closing devices 300, 300 are each suitably mounted on the swinging body of the machine, as by means of brackets 32!] rigidly secured there 43!], and

to and to the body, and the devices are so posijam nut 450 v a plunger 460, said 10 tioned that the rollers 520 bear upon the upper side of the base plate 5. The circuit closing device 300 which is responsive to increased loads on the machine, in this modified arrangement, is positioned at the forward side of the swinging axis of the machine, while the device 300' which is responsive to decreased loads, is positioned at the rearward side of the swinging axis which is represented by the center pin 4. Thus, whenever there is any change in the load, the swinging body of the machine will tend to tip forwardly, in the case of an increased load, closing the contacts of the circuit closing device 300, which in turn causes the counterweight 8 to move rearwardly ingpositions; and having of its .mass equally balanced about the axis of swing aforesaid when the for, variations of until it assumes a position which will balance the load. On the other hand, in the case of a decreasein load on the machine, the swinging body will tend to tip rearwardly, closing the contacts of the circuit closing device 300, which in turn causes the counterweight 8 to move forwardly until a condition of balance is reestablished.

It may be noted that while the hydraulic control valve unit l6 and the pump l9 have been illustrated as disposed within the tank or receptacle 22 containing the hydraulic fluid, this arrangement is not essential, and the control valve unit and the pump may be located at any convenient point on the machine and suitably connected up to the tank for the hydraulic fluid as the space limitations of the machine require or permit.

It may also be noted that the electrical circuit making and breaking devices of the electrical circuit are of the positively acting type, as illustrated in the drawings, and hence they are not affected by the working positions of the machine, as where the machine is operated on a grade or on uneven ground.

While the specific details have been herein shown and described, the invention is not confined thereto as changes and alterations may be made without departing from the spirit thereof as defined by the appended claims.

I claim:

1. Counterbalancing apparatus for load lifting and handling machines of the class described, which include a body which is mounted for swinging movements about a vertical axis, a unitary counterweight movably mounted on the body and shiftable towards and away from the vertical axis of swing of the body, whereby to compensate for variations of load on the machine, said counterweight having the weight distribution of its mass equally balanced about the axis of swing aforesaid when the counterweight is shifted to the limit of its movement in one direction.

2. Counterbalancing apparatus for load lifting and handling machines of the class described, which include a body which ismounted for swinging movements about a ertical axis, a unitary counterweight movably mounted on the body and shiftable towards and away from the vertical axis of swing of the'body, whereby to compensate load on the machine, said counterweight being located and confined wholly within the boundaries of the swinging body in all positions of its movements ranging between the effective maximum and minimum counterbalancthe weight distribution counterweight assumes its minimum effective counterbalancing IDOSitiOIl.

3. Counterbalancing apparatus for load lifting and handling machines of the class described, which include a body which is mounted 1 for swinging movements about a vertical axis, a counterweight movably mounted on the body and shiftable towards and away from the vertical axis of swing of the body, whereby to compensate for variations of load on the machine, hydraulic operating means including a shiftable hydraulic 'control valve which is selectively shiftable from a normally neutral position to increased and decreased load positions, respectively, for shifting said counterweight, and electrical control means automatically responsive to variations in load for controlling the operations of the hydraulic operating means aforesaid, and including circuit breaking means operable to render said electrical control means ineifective responsive to movement of the counterweight to the extreme limits of its -movement in either direction.

4. Apparatus as defined in claim 3, wherein the hydraulic operating means includes means for holding the counterweight in a condition of. rest when the counterweight assumes a load-balancing position.

.5. Apparatus as defined in claim 3, wherein the electrical control means includes a normally balanced electromagnetic valve positioning device for shifting the hydraulic control valve.

6. Counterbalancing apparatus for load lifting and handling machines of the class described, which include a body which is mounted for swinging movements about a vertical axis, a counterweight movably mounted on the body and shiftable towards and away from the vertical axis of swing of the body, whereby to compensate for variations of load on the machine, hydraulic jack means operatively connected to the counterweight for imparting movements thereto in either direction, a hydraulic control system for operating said jack means, including a shiftable control valve normally balanced in neutral position and movable in opposite directions to cause movement of the counterweight in respectively opposite positions, and an electrical control circuit for controlling the operation of said hydraulic control system, including electro-magnetic valve positioning means for shifting the valve aforesaid, together with circuit making and breaking means operable responsive to predetermined conditions of balance and unbalance of the machine for energizing and deenergizing the electromagnetic valve positioning means, and additional circuit making and breaking means operable by the counterweight for rendering the electric control circuit ineffective when the counterweight reaches the extreme limits of its movement in either direction.

'7. Counterbalancing apparatus for load lifting and handling machines of the class described, which include a body which is mounted for swinging movements about a vertical axis, a counterweight movably mounted on the body and shiftable towards and away from the vertical axis of swing of the body, whereby to compensate for variations of load on the machine, hydraulic jack means operatively connected to the counterweight for imparting movements thereto in either irection, a hydraulic control system for operating said jack means, an electrical control circuit for controlling the operation of said hydraulic control system, and means terrupting said electric control circuit responsive to variations of the load on the machine.

8. Counterbalancing apparatus for load lifting and handling machines of the class described, which include a body which is mounted for swinging movements about a vertical axis, a

for automatically in-' counterweight movably mounted on the body and shiftable towards and away from the vertical axis of swing of the body, whereby to compensate for variations of load on the machine, hydraulic jack means operatively connected to the counterweight for imparting movements thereto in either direction, a hydraulic control system for operating said jack means, said hydraulic control system including a shiftable control valve normally balanced in a neutral position and movable in opposite directions to cause movement of the counterweight in respectively opposite directions, and an electrical control circuit for controlling the operation of said hydraulic control system, said electrical control circuit including electromagnetic valve positioning means for shifting the control valve aforesaid, together with circuit making and breaking means operable responsive to predetermined conditions ofbalance and unbalance of the machine, for energizing and deenergizing the electromagnetic valve positioning means, said circuit making and breaking means being positioned on opposite sides of the axis of swing of the machine and being of the positively acting type.

9. Counterbalancing apparatus for load lifting and handling machines of the class described which include a body which is mounted for swinging movements about a vertical axis, a counterweight movably mounted on the body and shiftable towards and away from the vertical axis of swing of the body, whereby to compensate for variations of load on the machine, hydraulic jack means operatively connected to the counterweight for imparting movements thereto in either direction, a hydraulic control system for operating said jack means, said hydraulic control system including a shiftable control valve normally balanced in a neutral position and movable in opposite directions to cause movement of the counterweight in respectively opposite directions, and an electrical control circuit for controlling the operation of said hydraulic control system, said electrical control circuit including electromagnetic valve positioning means for shifting the control valve aforesaid, together with circuit making and breaking means operable responsive to. predetermined conditions of balance and unbalance of the machine, for energizing and dc energizing the electromagnetic valve positioning means, and additional circuit making and breaking means operable by the counterweight for rendering the electrical control circuit ineifective when the counterweight reaches the extreme limits of its movements in either direction, said additional circuit making and breaking means having the form of a pair of push type switches respectively disposed in the path of movement of the counterweight at the extreme limits of movement of the counterweight in each direction so that the switches will be engaged and operated by the counterweight when it reaches the limits of its movements.

GEORGE E. TANGUY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

